Red phosphor, method for producing red phosphor, white light source, illuminating device, and liquid crystal display device

ABSTRACT

A compound is provided containing silicon, aluminum, strontium, europium, nitrogen, and oxygen is used that enables a red phosphor having strong luminous intensity and high luminance to be obtained, and that enables the color gamut of a white LED to be increased with the use of the red phosphor. The red phosphor contains an element A, europium, silicon, aluminum, oxygen, and nitrogen at the atom number ratio of the following formula: [A (m−x) Eu x ]Si 9 Al y O n N [12+y−2(n−m)/3] . The element A in the formula is at least one of magnesium, calcium, strontium, and barium, and m, x, y, and n in the formula satisfy the relations 3&lt;m&lt;5, 0&lt;x&lt;1, 0&lt;y&lt;2, and 0&lt;n&lt;10.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage of International ApplicationNo. PCT/JP2009/062244 filed on Jun. 30, 2009 and which claims priorityto Japanese Patent Application No. JP2008-173467 filed on Jul. 2, 2008and Japanese Patent Application No. JP2009-122757 filed on May 21, 2009,the entire contents of which are being incorporated herein by reference.

BACKGROUND

The present disclosure relates to a red phosphor, and a method ofproduction thereof, and to white light sources, illuminating devices,and liquid crystal display devices using a red phosphor.

A white light source formed of a light-emitting diode is used as thebacklight of illuminating devices and liquid crystal display devices. Aknown example of such a white light source is one in which acerium-containing yttrium aluminum garnet (hereinafter, “YAG:Ce”)phosphor is disposed on the emission side of a blue-emitting diode(hereinafter, “blue LED”).

As another example, those including green and red sulfide phosphorsdisposed on the emission side of a blue LED are known (see, for example,Patent Document 1). Further, there has been proposed a configuration inwhich a fluorescent material prepared as a solid solution of elementssuch as Mn and Eu in a CaAlSiN₃ crystal is disposed on the emission sideof a blue-purple- or blue-glowing LED with another fluorescent materialat a predetermined proportion (see, for example, Patent Document 2).

Patent Document 1: JP-A-2002-60747

Patent Document 2: Japanese Patent No. 3931239

However, because the white light source including the YAG:Ce phosphordisposed on the emission side of the blue LED lacks a red component inthe YAG:Ce phosphor emission spectrum, the white light appears bluish,and the color gamut is narrow. Thus, it is difficult to produce purewhite illumination with illuminating devices that use such a white lightsource. Further, display with desirable color reproducibility isdifficult to achieve with a liquid crystal display device that uses sucha white light source as the backlight.

In the white light source including the green and red sulfide phosphorsdisposed on the emission side of the blue LED, luminance degradesovertime because the sulfide red phosphor undergoes hydrolysis. It istherefore difficult to produce high-quality illumination or display ofnon-degrading luminance with an illuminating device or a liquid crystaldisplay device that uses such a white light source.

The white light source using the fluorescent material prepared as asolid solution of elements such as Mn and Eu in a CaAlSiN₃ crystal islaborious, because it uses and mixes two kinds of fluorescent material.

It is therefore desired to provide a red phosphor of strong luminousintensity and high luminance, a method of production thereof, a whitelight source and an illuminating device that use the red phosphor andproduce pure white illumination, and a liquid crystal display devicethat has desirable color reproducibility.

SUMMARY

In order to achieve the foregoing object, a red phosphor of anembodiment contains an element A, europium (Eu), silicon (Si), aluminum(Al), oxygen (O), and nitrogen (N) in the proportions of the compositionformula (1)[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1),where the element A in the composition formula (1) is at least one ofmagnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Further,in the composition formula (1), m, x, y, and n in the compositionformula (1) satisfy the relations 3<m<5, 0<x<1, 0<y<2, and 0<n<10.

By the inclusion of strontium and europium, the red phosphor of theconfiguration above is capable of red emission, and, because of theforegoing composition, luminous intensity is strong and luminance ishigh. It was confirmed that the red phosphor was capable of producing aluminous intensity about 1.5 times higher than that of the YAG:Cephosphor at the emission peak wavelength of, for example, 662 nm.

A producing method of such a red phosphor according to an embodiment, isalso provided. A carbonate compound of element A, europium nitride,silicon nitride, and aluminum nitride are prepared so as to contain theelement A, europium (Eu), silicon (Si), and aluminum (Al) at theproportions of the composition formula (1). These are mixed withmelamine to produce a mixture. The mixture is calcined, and theresulting calcined product is pulverized. As a result, the red phosphorof the composition formula (1) can be obtained.

In an embodiment a white light source is provided in which a kneadedproduct of the red phosphor and a green phosphor in a transparent resinis disposed on a blue-emitting diode, an illuminating device thatincludes a plurality of such white light sources on a substrate, and aliquid crystal display device that uses the white light source as thebacklight of a liquid crystal display panel.

Because the red phosphor of the embodiment is used, the white lightsource of the present invention has a peak emission wavelength in thered waveband (for example, 640 nm to 770 nm waveband), and has strongluminous intensity and high luminance. As a result, bright white lightof three primary colors including the blue light by the blue-emittingdiode, the green light by the green phosphor, and the red light by thered phosphor can be obtained. The illuminating device and the backlightusing such a white light source are therefore capable of producingillumination and display with bright white emission.

As described above, with the emission peak wavelength in the redwaveband, the red phosphor of the present invention is capable of redemission, and has stronger luminous intensity and higher luminance thanthose of the conventional phosphor.

Because the white light source of the embodiment uses the red phosphorof the present invention that has an emission peak wavelength in the redwaveband, and that possesses stronger luminous intensity and higherluminance than those of the conventional red phosphor, bright whitelight with a wide color gamut can be advantageously obtained.

Because the illuminating device of the embodiment uses the white lightsource of the present invention, bright white light with a wide colorgamut can be obtained, and thus high-luminance pure white illuminationcan be produced.

The liquid crystal display device of the embodiment uses the white lightsource of the present invention as the backlight that illuminates theliquid crystal display panel, and thus the liquid crystal display panelcan be illuminated with bright white light of a wide color gamut. Thus,high-luminance pure white can be obtained on the display screen of theliquid crystal display panel, and high-quality display with superiorcolor reproducibility can be performed.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram representing an example of emission spectra of redphosphors of an embodiment.

FIG. 2 is a diagram representing the Eu concentration dependence of theemission characteristics of a red phosphor of the embodiment.

FIG. 3 is a diagram explaining the Eu concentration dependence of thechromaticity (X, Y) of a red phosphor of the embodiment.

FIG. 4 represents the emission spectrum of each red phosphor of theembodiment after being normalized at the maximum peak=1 cps/nm (part 1).

FIG. 5 represents the emission spectrum of each red phosphor of theembodiment after being normalized at the maximum peak=1 cps/nm (part 2).

FIG. 6 represents the emission spectrum of each red phosphor atdifferent atom number ratios y of aluminum (Al) in composition formula(1).

FIG. 7 is a diagram representing optical characteristic values fordifferent aluminum composition ratios [y/(9+y)] with respect to thetotal composition ratio of silicon (Si) and aluminum (Al) based on FIG.6.

FIG. 8 is a diagram representing the relationship between the calciumcontent in a red phosphor of the embodiment and luminous intensity.

FIG. 9 is a diagram representing the temperature characteristics of redphosphors produced in Examples.

FIG. 10 is a flowchart representing an embodiment of a red phosphorproducing method of the embodiment.

FIG. 11 is a schematic cross sectional view representing an embodimentof a white light source of the embodiment.

FIG. 12 is a diagram representing an example of an emission spectrum ofa white light source of the embodiment.

FIG. 13 is a schematic plan view representing an embodiment of anilluminating device of the embodiment.

FIG. 14 is a schematic block diagram representing an embodiment of aliquid crystal display device of the embodiment.

FIG. 15 is an HAADF-STEM image of a red phosphor produced in an Example.

FIG. 16 represents a TEM-EDX analysis spectrum at each point of the redphosphor produced in the Example.

FIG. 17 represents a TEM-EDX analysis spectrum at each point of the redphosphor produced in the Example.

FIG. 18 is a magnified view of the HAADF-STEM image of FIG. 15.

FIG. 19 represents the XDR analysis spectrum of each red phosphorproduced in Examples.

FIG. 20 is a diagram representing the relationship between luminousintensity ratio and the amount of melamine added in the production of ared phosphor.

FIG. 21 is a diagram representing the relationship between luminousintensity ratio and the heating temperature in a first heat-treatmentstep for the production of a red phosphor.

FIG. 22 is a diagram representing the relationship between peak luminousintensity ratio and the amount of melamine added in the production of ared phosphor.

FIG. 23 is a diagram representing the relationship between relativeluminance ratio and the amount of melamine added in the production of ared phosphor.

FIG. 24 is a diagram representing the relationship between the amount ofmelamine added in the production of a red phosphor, and the amount ofoxygen remaining in the red phosphor.

FIG. 25 is a diagram representing the relationship between the amount ofmelamine added in the production of a red phosphor, and the amount ofcarbon remaining in the red phosphor.

FIG. 26 is a diagram representing the relationship between the amount ofmelamine added in the production of a red phosphor, and the averageparticle size of the red phosphor.

FIG. 27 is a diagram representing the relationship between the amount ofeuropium nitride added in the production of a red phosphor, and the peakluminous intensity ratio of the red phosphor.

FIG. 28 is a diagram representing the relationship between the amount ofeuropium nitride added in the production of a red phosphor, and therelative luminance ratio of the red phosphor.

FIG. 29 is a diagram representing ratios with varying component ratiosof strontium carbonate, europium nitride, and silicon nitride underfixed component ratios of melamine and aluminum nitride.

FIG. 30 is a diagram representing the X-ray diffraction pattern of a redphosphor produced by a producing method of the embodiment.

DETAILED DESCRIPTION

Embodiments are described below with reference to the accompanyingdrawings, in the following order.

1. First Embodiment (configuration of red phosphor)

2. Second Embodiment (red phosphor producing method)

3. Third Embodiment (exemplary configuration of white light source)

4. Fourth Embodiment (exemplary configuration of illuminating device)

5. Fifth Embodiment (exemplary configuration of liquid crystal displaydevice)

1. First Embodiment (Configuration of Red Phosphor)

The red phosphor is a compound that contains an element A, europium(Eu), silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N) at theproportions of the composition formula (1) below.[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1),

The element A in the composition formula (1) is at least one ofmagnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and maybe more than one kind of these elements. Preferably, strontium (Sr) isused for element A. By containing calcium (Ca) as element A, theemission peak wavelength of the red phosphor can be controlled accordingto the calcium (Ca) content, as will be described later.

In the composition formula (1), m, x, y, and n satisfy the relations3<m<5, 0<x<1, 0<y<2, and 0<n<10.

The atom number ratio of the nitrogen (N) [12+y−2(n−m)/3] in thecomposition formula (1) is calculated so that the sum of the atom numberratio of each element in the composition formula (1) becomes neutral.Specifically, when the atom number ratio of the nitrogen (N) in thecomposition formula (1) is α, and when the charge of each element in thecomposition formula (1) is compensated, the following equation isobtained.2(m−x)+2x+4×9+3y−2n−3α=0

From this, the atom number ratio of the nitrogen (N) can be calculatedas follows.α=12+y−2(n−m)/3

The red phosphor of composition formula (1) is a compound of a crystalstructure that belongs to an orthorhombic system spatial point groupPmn21, specifically, a configuration in which some of the silicon (Si)atoms are replaced with aluminum (Al) in the crystal structure.

The characteristics of the red phosphor of such a configuration aredescribed below.

Optical Characteristics

FIG. 1 represents the emission spectra of red phosphors (1) to (7) ofthe composition formula (1) using strontium (Sr) for element A. Forcomparison, the emission spectrum of a conventional YAG:Ce phosphor isalso presented. Table 1 below presents the optical characteristic valuesof the red phosphors (1) to (7) of the composition formula (1) takenfrom the emission spectra of FIG. 1. The measurement values are based onirradiation of 450-nm excitation light with a FLUOROLOG3 (SPEX).

TABLE 1 Eu Peak Luminous Luminous concentration wavelength intensityratio intensity ratio Chromaticity Chromaticity Sample No. (x/m) (nm)(vs. YAG) (vs. YAG) X Y (1) 17.228% 664 1.39 0.20 0.678 0.321 (2)16.226% 667 1.42 0.21 0.677 0.322 (3) 15.029% 662 1.48 0.22 0.677 0.323(4) 11.175% 659 1.51 0.26 0.671 0.328 (5) 7.514% 648 1.58 0.34 0.6610.338 (6) 3.661% 636 1.74 0.47 0.648 0.351 (7) 1.156% 626 1.66 0.590.627 0.372

As can be seen in FIG. 1 and Table 1, the luminous intensity at the peakwavelength is about 1.5 times higher in the red phosphors (1) to (7) ofthe composition formula (1) range than in the conventional YAG:Cephosphor. The peak wavelength is 620 nm to 670 nm, showing thatdesirable red emission is obtained compared with the yellow in theconventional YAG:Ce phosphor.

Particularly desirable red emission is obtained in the vicinity of thepeak wavelength 660 nm of the emission spectrum in the red phosphors (1)to (3) of the range 0.5<x<1 in the composition formula (1).

In the red phosphors (4) to (7) of the range 0<x<0.5 in the compositionformula (1), high luminous intensity emission can be obtained at thepeak wavelength of the emission spectrum.

Eu Concentration Dependence of Emission Characteristics

FIG. 2(1) represents the luminous intensity of the red phosphor of thecomposition formula (1) range as a function of the ratio x/m of m and xin the composition formula (1), relative to the conventional YAG:Cephosphor. It can be seen from FIG. 2(1) that the red phosphor ofcomposition formula (1) has a luminous intensity peak near x/m=3.75%,demonstrating that the luminous intensity varies with the concentrationof europium (Eu). Preferably, x/m≦11% for the red phosphor ofcomposition formula (1), because it yields a luminous intensity 1.5times higher than that of the conventional YAG:Ce phosphor. It can beseen that the highest luminous intensity can be obtained near x/m=3.75%.

FIG. 2(2) represents the relative luminance of the red phosphor of thecomposition formula (1) range as a function of the ratio x/m of m and xin the composition formula (1), relative to the conventional YAG:Cephosphor. It can be seen from FIG. 2(2) that the relative luminance ofthe red phosphor of composition formula (1) decreases with increase ineuropium (Eu) concentration, as the emission wavelength peak shiftshigher.

Eu Concentration Dependence of Chromaticity

FIG. 3 represents the chromaticity (X,Y) of each red phosphor ofcomposition formula (1). The europium (Eu) concentration in each redphosphor was varied by setting a different ratio x/m of m and x withinthe range of composition formula (1). It can be seen from FIG. 3 thatthe chromaticity (X,Y) shifts towards the (+X,−Y) side as the relativeeuropium (Eu) concentration with respect to element A [strontium (Sr)]is increased. This demonstrates that the chromaticity of each redphosphor of the composition formula (1) can be controlled by theeuropium (Eu) concentration with respect to element A [strontium (Sr)].

Al Concentration Dependence of Peak Wavelength

FIGS. 4 and 5 represent the emission spectrum of each red phosphor ofcomposition formula (1). The data have been normalized at the maximumpeak=1 cps/nm. The data in FIGS. 4 and 5 represent the emission spectraof the red phosphors of varying atom number ratios y of aluminum (Al)within the range of composition formula (1). For comparison, the dataalso includes the emission spectrum of a compound whose atom numberratio y of aluminum (Al) falls outside of the range 0<y<2 of compositionformula (1).

It can be seen from the data that the luminous intensity peak of the redphosphor of composition formula (1) tends to shift towards the longerwavelength side as the aluminum (Al) concentration is increased.

FIG. 6 represents the emission spectra of red phosphors of varying atomnumber ratios y of aluminum (Al) in the composition of compositionformula (1). For comparison, the data also includes the emissionspectrum of a compound whose atom number ratio y of aluminum (Al) fallsoutside of the range 0<y<2 of composition formula (1). FIG. 7 representsoptical characteristic values at different aluminum composition ratios[y/(9+y)] with respect to the total composition ratio of silicon (Si)and aluminum (Al), based on FIG. 6.

As can be seen from the peak wavelengths in FIG. 7(1), the luminousintensity peak tends to shift towards the longer wavelength side as thealuminum (Al) composition ratio [y/(9+y)], specifically, the aluminumconcentration, is increased in the material of composition formula (1).

Further, as can be seen from the peak intensities in FIG. 7(2), the peakintensity is held high at 0<[y/(9+y)]<18.2, which corresponds to therange 0<y<2 of the atom number ratio of aluminum in composition formula(1). Specifically, the peak intensity is held high at the range y<2 ofthe composition formula (1) of the embodiment. It should be noted thatsamples with lower peaks have large half bandwidths, and high peakintensities are maintained at [y/(9+y)]<18.2, as confirmed by integralvalues.

Further, as can be seen from the half bandwidths in FIG. 7(3), the halfbandwidth of the emission spectrum becomes wider as the aluminum (Al)composition ratio [y/(9+y)], specifically, the aluminum concentration,increases in the material of composition formula (1).

Element A Dependence of Peak Wavelength

FIG. 8 represents the emission spectra of red phosphors at varyingproportions of strontium (Sr) and calcium (Ca) used for the element A ofcomposition formula (1). As can be seen in FIG. 8, the emission peakwavelength was 664 nm when Ca/Sr=0, specifically, when calcium (Ca) wasnot contained. The emission peak wavelength was 678 nm at Ca/Sr=0.27,specifically, when the calcium content was 0.27 with respect to thestrontium 1. The emission peak wavelength was 679 nm at Ca/Sr=0.41,specifically, when the calcium content was 0.41 with respect to thestrontium 1. The emission peak wavelength was 684 nm at Ca/Sr=0.55,specifically, when the calcium content was 0.55 with respect to thestrontium 1.

As demonstrated above, when calcium (Ca) is contained as element A inthe composition formula (1), the emission peak wavelength of the redphosphor represented by the composition formula (1) can be shiftedtowards the longer wavelength side by increasing the calcium (Ca)content.

Temperature Characteristics

FIG. 9 represents the temperature characteristic of red phosphor (9) ofcomposition formula (1). For comparison, the figure also presents thetemperature characteristic of phosphor (9′) that does not containaluminum (y=0; outside the range of composition formula (1)), and thetemperature characteristic of a conventional YAG:Ce phosphor.

As can be seen from FIG. 9, the percentage maintenance of luminousintensity under heating conditions is higher in the red phosphor ofcomposition formula (1) than in the aluminum-free phosphor (9′) and theconventional YAG:Ce phosphor, showing that the red phosphor ofcomposition formula (1) has a more desirable temperature characteristic.

This result can be explained by the lack of the hydrolysis that occursin the conventional sulfide red phosphor, and by the presence ofaluminum (Al) in the crystal structure. Specifically, the result appearsto be linked to the increased distance between the europium (Eu) atomsas a result of elongated c axis following the replacement of the silicon(Si) with Al in the crystal structure that belongs to the orthorhombicsystem spatial point group Pmn21 represented by composition formula (1).

Other

The red phosphor of composition formula (1) may contain carbon (C). Thecarbon (C) is an element that originates in the raw material of the redphosphor producing process, and may be left over in the synthesizedmaterial forming the red phosphor, without being removed during thesynthesis. The carbon (C) serves to remove the excess oxygen (O) in theprocess, and thus to adjust the oxygen amount.

Variation 1 of Red Phosphor

In the red phosphor, selenium (Ce) may be used instead of the europium(Eu) in the composition formula (1). In this case, the red phosphorcontains the charge-compensating lithium (Li), sodium (Na), andpotassium (K) atoms, in addition to the selenium (Ce).

Variation 2 of Red Phosphor

In the foregoing First Embodiment, the red phosphor was described as thecompound of composition formula (1) that contains aluminum. However, avariation of the red phosphor may be, for example, an aluminum-freecompound that contains silicon, strontium, europium, nitrogen, andoxygen. Such a compound is represented by the following compositionformula (2).[Sr_((m−x))Eu_(x)]Si₉O_(n)N_([12−2(n−m)/3])  Composition Formula (2)

In the composition formula (2), x, m, and n satisfy the relations0.5<x<1.0, 3.5<m<4.0, and 0<n<13.0.

Note that the atom number ratio [12+y31 2(n−m)/3] of the nitrogen (N) inthe composition formula (2) is calculated so that the sum of the atomnumber ratio of each element in the composition formula (2) isneutralized.

The red phosphor of composition formula (2) may contain calcium (Ca). Byincreasing the content of calcium with respect to strontium, theemission peak wavelength of the red phosphor of composition formula (2)can be shifted towards the longer wavelength side.

Further, the red phosphor of composition formula (2) may contain carbon.The carbon serves to remove the excess oxygen (O) in the process, andthus to adjust the oxygen amount.

The red phosphor of composition formula (2) has the same effects as thered phosphor of composition formula (1), and additionally providesbetter ease of handling owning to the fewer constituent elements.Another advantage is the simpler crystal structure, and thus fewerdefects. However, the red phosphor of composition formula (1) hassuperior heat resistance, as described with reference to FIG. 9.

2. Second Embodiment (Red Phosphor Producing Method)

An embodiment of a method of production of the red phosphor ofcomposition formula (1) is described below with reference to theflowchart of FIG. 4.

As represented in FIG. 3, a raw material mixing step S1 is performedfirst. The characteristic feature of the raw material mixing step isthat the raw material melamine (C₃H₆N₆) is used and mixed with the rawmaterial compounds that contain the constituent elements of compositionformula (1).

The raw material compounds containing the constituent elements ofcomposition formula (1) are prepared as the carbonate compound ofelement A [for example, strontium carbonate (SrCO₃)], europium nitride(EuN), silicon nitride (Si₃N₄), and aluminum nitride (AlN). Eachcompound is then weighed in a predetermined molar ratio, so that thecomposition formula (1) element contained in each raw material compoundhas the atom number ratio of composition formula (1). After beingweighed, the compounds are mixed to produce a mixture.

The melamine is added under the flux at a predetermined proportion withrespect to the sum of the total number of moles of the strontiumcarbonate, europium nitride, silicon nitride, and aluminum nitride(AlN).

The mixture is produced, for example, by mixing the compounds in anagate mortar, inside a glow box placed in a nitrogen atmosphere.

Thereafter, a first heat-treatment step S2 is performed. In the firstheat-treatment step, the mixture is calcined to produce a first calcinedproduct as a precursor of the red phosphor. For example, the mixture issubjected to heat treatment in a hydrogen (H₂) atmosphere inside a boronnitride crucible. The first heat-treatment step involves, for example, a2-hour heat treatment at a temperature of 1,400° C. The heat treatmenttemperature and the heat treatment time can be appropriately varied, aslong as the mixture is calcined.

In the first heat-treatment step, the melamine, with the melting pointof 250° C. or less, undergoes pyrolysis. The pyrolysis produces carbon(C) and hydrogen (H), which bind to some of the oxygen (O) atomscontained in the strontium carbonate, and form a carbon oxide gas (CO orCO₂) or H₂O. The carbon oxide gas (CO or CO₂) or H₂O evaporates, and areremoved from the first calcined product. The nitrogen (N) contained inthe decomposed melamine promotes reduction and nitridation.

The next step is a first pulverizing step S3. In the first pulverizingstep, the first calcined product is pulverized to produce a firstpowder. For example, the first calcined product is pulverized in a glowbox placed in a nitrogen atmosphere, using an agate mortar, and passedthrough, for example, a #100 mesh (opening size of about 200 μm) toobtain a first calcined product having an average particle size of 3 μmor less. This helps suppress nonuniformity in the components of a secondcalcined product produced in the next second heat treatment step.

Then, a second heat-treatment step S4 is performed. In the secondheat-treatment step, the first powder is subjected to heat treatment toproduce a second calcined product. For example, the first powder issubjected to heat treatment in a nitrogen (N₂) atmosphere inside a boronnitride crucible. In the second heat-treatment step, the heat treatmentis performed for, for example, 2 hours under the pressurized nitrogenatmosphere of 0.85 MPa, and at the heat treatment temperature of 1,800°C. The heat treatment temperature and heat treatment time can beappropriately varied, as long as the first powder is calcined.

As a result of the second heat-treatment step, the red phosphor ofcomposition formula (1) is obtained. The second calcined product (redphosphor) obtained in the second heat-treatment step is a homogeneousproduct according to composition formula (1).

The next step is a second pulverizing step S5. In the second pulverizingstep, the second calcined product is pulverized to produce a secondpowder. For example, the second calcined product is pulverized in a glowbox placed in a nitrogen atmosphere, using an agate mortar, followed bypulverization to make the average particle size, for example, about 3.5μm, using, for example, a #420 mesh (opening size of about 26 μm).

By the red phosphor producing method, a fine powder (for example, anaverage particle size of about 3.5 μm) of red phosphor is obtained. Bythus forming the red phosphor in the form of a powder, the red phosphorcan be uniformly kneaded into a transparent resin with, for example, agreen phosphor powder.

As a result, the red phosphor of composition formula (1) is obtainedthat contains each element mixed at the atom number ratio of the rawmaterial mixing step S1.

Variation of Red Phosphor Producing Method

The producing method described with reference to the flowchart of FIG. 4is also applicable to the producing method of the red phosphor as thealuminum (Al)-free compound of composition formula (2).

In the producing method (second producing method), a mixture ofstrontium carbonate, silicon nitride, europium nitride, and melamine isproduced, and the mixture is calcined to produce a precursor of the redphosphor. Here, the melamine is decomposed, and the carbon and hydrogencontained therein bind to the oxygen in the strontium carbonate,forming, for example, carbon oxide gas or H₂O, and thus removing some ofthe oxygen atoms in the strontium carbonate.

The first calcined product is then pulverized to produce a first powder,which helps suppress nonuniformity in the components of the secondcalcined product produced in the next second heat-treatment step.

The first powder is then subjected to heat treatment to produce a secondcalcined product. The second calcined product (red phosphor) obtained inthe second heat-treatment step is therefore a homogenous productaccording to the composition formula (2).

The second calcined product is further pulverized to produce a secondpowder. By forming the red phosphor in the form of a powder, the redphosphor can be uniformly kneaded into a transparent resin with, forexample, a green phosphor powder.

The red phosphor obtained after these steps has a peak emissionwavelength in the red waveband (for example, a 640 nm to 770 nmwaveband), as will be described in Examples.

By excluding aluminum nitride from the raw material, ease of handlingimproves owning to the fewer constituent elements. Another advantage isthe simpler crystal structure, and thus fewer defects.

3. Third Embodiment (Exemplary Configuration of White Light Source)

An embodiment of a white light source is described below with referenceto the schematic cross sectional view of FIG. 11.

As illustrated in FIG. 11, a white light source 1 includes ablue-emitting diode 21 on a pad portion 12 formed on an elementsubstrate 11. Electrodes 13 and 14 that supply driving power to theblue-emitting diode 21 are formed on the element substrate 11 by beinginsulated from the element substrate 11. The electrodes 13 and 14 areconnected to the blue-emitting diode 21, for example, via leads 15 and16, respectively.

For example, a resin layer 31 is provided around the blue-emitting diode21. The resin layer 31 has an aperture 32 for the blue-emitting diode21. The aperture 32 has a slant face forming an aperture area thatbecomes wider along the emission direction of the blue-emitting diode21. A reflecting film 33 is formed on the slant face. Specifically, thereflecting film 33 covers the wall surface of the aperture 32 having aform of a mortar in the resin layer 31, and the blue-emitting diode 21is disposed on the bottom surface of the aperture 32. A kneaded product43 as a kneaded product of a red phosphor and a green phosphor in atransparent resin is embedded in the aperture 32, covering theblue-emitting diode 21 to form the white light source 1.

A characteristic feature of the white light source 1 is that the redphosphor of composition formula (1) of the present invention is used asthe red phosphor.

As an example of the red phosphor, a compound of the composition formula(Sr_(3.4)Eu_(0.7))Si₉Al_(0.7)O_(0.7)N₁₅ using strontium (Sr) as the (1)was used, where m=4.1, x=0.7, y=0.7, and n=0.7.

As the green phosphor, a compound of the composition formula(Sr,Ba)₂SiO₄:Eu was used, for example.

The kneaded product 43 was made by kneading 0.015 g of the red phosphorand 0.45 g of the green phosphor in a silicone resin. For example, theproduct Silicone KJR637 (refractive index 1.51) from Shin-Etsu ChemicalCo., Ltd. was used as the silicone resin. The characteristics of thewhite light source 1 fabricated as above are as follows.

Current value=40 mA, and current density=327 mA/mm² under appliedvoltage of 3.235 V to the blue-emitting diode 21. The opticalcharacteristics are as follows. Radiant flux=31.1 mW, WPE=0.240,Lms=6.8, 1 m/W=52.7, chromaticity (x)=0.2639, and chromaticity(y)=0.2639. WPE denotes the energy efficiency, Lms the lumen:luminousflux, and 1 m/W the emission efficiency.

The emission spectrum had blue (450 nm), green (534 nm), and red (662nm) wavelength peaks, as represented in FIG. 12.

As described above, the red phosphor of the present invention has a peakemission wavelength in the red waveband (for example, 640 nm to 770 nmwaveband), and thus has strong luminous intensity and high luminance. Asa result, bright white light of three primary colors including the bluelight by the blue LED, the green light by the green phosphor, and thered light by the red phosphor can be obtained.

The white light source 1 therefore advantageously produces bright whitelight with a wide color gamut.

4. Fourth Embodiment (Exemplary Configuration of Illuminating Device)

An embodiment of an illuminating device is described below withreference to the schematic plan view of FIG. 13.

As illustrated in FIG. 13, an illuminating device 5 includes a pluralityof white light sources 1 on an illumination substrate 51. The whitelight source 1 is that described in FIG. 11. The white light sources 1may be disposed, for example, in a square grid array as in FIG. 13(1),or each row may be shifted, for example, ½ pitch, as illustrated in FIG.13(2). The shift pitch is not limited to ½, and may be ⅓ or ¼. The shiftmay occur row by row, or in units of plural rows (for example, tworows).

Alternatively, each column may be shifted, for example, ½ pitch, thoughnot illustrated. The shift pitch is not limited to ½, and may be ⅓ or ¼.The shift may occur row by row, or in units of plural rows (for example,two rows).

In other words, the white light sources 1 may be shifted in any ways.

The white light sources 1 have the configuration described withreference to FIG. 11. Specifically, the white light sources 1 includethe kneaded product 43 of the red phosphor and the green phosphor in atransparent resin on the blue-emitting diode 21.

A characteristic feature of the white light sources 1 is that the redphosphor of composition formula (1) of the embodiment is used as the redphosphor.

Because of the white light sources 1 substantially equivalent of pointemission are horizontally and vertically disposed on the illuminationsubstrate 51, the illuminating device 5 becomes equivalent of surfaceemission. This enables the illuminating device 5 to be used as thebacklight of, for example, a liquid crystal display device. Theilluminating device 5 also can be used as a wide variety of illuminatingdevices, including ordinary illuminating devices, illuminating devicesfor shooting, and illuminating devices for construction sites.

Because the white light source 1 of the present invention is used, theilluminating device 5 can produce bright white light with a wide colorgamut. For example, when used as the backlight of a liquid crystaldisplay device, the illuminating device 5 can advantageously providehigh-luminance pure white on a display screen, and thus improves thedisplay screen quality.

5. Fifth Embodiment (Exemplary Configuration of Liquid Crystal DisplayDevice

An embodiment of a liquid crystal display device is described below withreference to the schematic block diagram of FIG. 14.

As illustrated in FIG. 14, a liquid crystal display device 100 includesa liquid crystal display panel 110 having a transmission displayportion, and a backlight 120 provided on the back side of the liquidcrystal display panel 110 (the surface opposite the display face). Theilluminating device 5 described with reference to FIG. 13 is used as thebacklight 120.

Because the illuminating device 5 of the embodiment is used as thebacklight 120, the liquid crystal display panel 110 of the liquidcrystal display device 100 can be shone upon by the wide color-gamut,bright white light of the three primary colors. Thus, high-luminancepure white can be obtained on the display screen of the liquid crystaldisplay panel 110, advantageously providing desirable colorreproducibility and improving display screen quality.

EXAMPLES Example 1

A red phosphor of composition formula (1), and a compound (phosphor)outside of the composition formula (1) were synthesized in Example 1 ofthe embodiment and in Comparative Example, respectively, according tothe procedure described with reference to the flowchart of FIG. 10, asfollows.

First, the raw material mixing step S1 was performed. Here, strontiumcarbonate (SrCO₃), europium nitride (EuN), silicon nitride (Si₃N₄),aluminum nitride (AlN), and melamine (C₃H₆N₆) were prepared. Each rawmaterial compound prepared as above was weighed at the molar ratiopresented in Table 2 below, and was mixed in a glow box placed in anitrogen atmosphere, using an agate mortar. It should be noted that themolar ratio of melamine is the percentage with respect to the sum of thetotal number of moles of the other compounds.

TABLE 2 Sample SrCO₃ EuN Si₃N₄ AlN Melamine No. (mol %) (mol %) (mol %)(mol %) (mol %) Composition (1) 44.2% 9.2% 36.8%  9.8% 60% m = 4.35, x =0.75, y = 0.8 (2) 44.4% 8.6% 37% 9.9% 60% m = 4.30, x = 0.70, y = 0.8(3) 44/1% 7.8% 39% 9.1% 60% m = 4.00, x = 0.60, y = 0.7 (4) 46.1% 5.8%39% 9.1% 60% m = 4.00, x = 0.45, y = 0.7 (5)  48% 3.9% 39% 9.1% 60% m =4.00, x = 0.30, y = 0.7 (6)  50% 1.9% 39% 9.1% 50% m = 4.00, x = 0.15, y= 0.7 (7) 51.3% 0.6% 39% 9.1% 50% m = 4.00, x = 0.05, y = 0.7

Next, the first heat-treatment step S2 was performed. Here, the mixturewas placed in a boron nitride crucible, and a 2-hour heat treatment wasperformed in a hydrogen (H₂) atmosphere at 1,400° C.

This was followed by the first pulverizing step S3. Here, the firstcalcined product was pulverized in a glow box placed in a nitrogenatmosphere, using an agate mortar, and passed through a #100 mesh(opening size of about 200 μm), so as to obtain the first calcinedproduct having an average particle size of 3 μm or less.

Next, the second heat-treatment step S4 was performed. Here, the powderof the first calcined product was placed in a boron nitride crucible,and a 2-hour heat treatment was performed in a 0.85-MPa nitrogen (N₂)atmosphere at 1,800° C. As a result, the second calcined product wasobtained.

This was followed by the second pulverizing step S5, in which the secondcalcined product was pulverized in a glow box placed in a nitrogenatmosphere, using an agate mortar. The second calcined product waspulverized to make the average particle size about 3.5 μm, using a #420mesh (opening size of about 26 μm).

By the red phosphor producing method, a fine powder of red phosphor (forexample, an average particle size of about 3.5 μm) was obtained.

The red phosphor produced as above was analyzed by ICP. The analysisconfirmed that each constituent element of the composition formula (1)in the red phosphor was contained at almost the same molar ratio (atomnumber ratio) as that in the raw material compound. It was alsoconfirmed that the red phosphor of the composition formula (1) wasobtained as presented in Table 2. Note that the red phosphors with thesample numbers (1) to (7) produced in Example 1 are the red phosphors(1) to (7) presented in Table 1 and in FIG. 1. The red phosphors (1) to(7) of the composition formula (1) range had the peak-wavelengthluminous intensity about 1.5 times higher than that of the conventionalYAG:Ce phosphor, and produced desirable red emission, as described withreference to FIG. 1.

Example 2

In Example 2, a red phosphor of the compositionSr_(3.4)Eu_(0.7)Si₉Al_(0.7)O_(0.7)N₁₀ (m=4.1, x=0.7, y=0.7, n=0.7) as anexample of the composition formula (1) was produced according to theprocedure described in Example 1. Note that, in Example 2, thecomposition ratio 10 of the nitrogen is not in accord with the[12+y−2(n−m)/3] of composition formula (1). This is due to the poorreliability of the measured oxygen and nitrogen concentration values bythe ICP analysis. ICP analysis, however, is highly reliable with regardto Sr, Eu, Si, and Al measurements, and, considering the chargecompensation based on the Sr, Eu, Si, and Al values, the result for thecomposition of the composition formula (1) is unquestionable.

TEM-EDX analysis was performed for the red phosphors produced as above.FIG. 15 shows an HAADF-STEM image with the analysis points in a redphosphor particle. As shown in FIG. 15, TEM-EDX analysis was performedat six locations, including points 1 to 4 within the same particle, andpoints 5 and 6 in another particle. FIGS. 16 and 17 present the results.

From the observation that the HAADF-STEM image in FIG. 15 had a uniformcontrast, and that there was no large difference in the EDX profile forthe points 1 to 4 in the same particle as presented in FIG. 16, it wasconformed that the element composition, including aluminum (Al), had nobias within the particle, and was substantially uniform. Further, aspresented in FIG. 17, the EDX profile did not greatly differ in anotherparticle, and formation of particles with substantially uniformcomposition ratios was confirmed. Note that copper (Cu) was detectedbecause of the TEM stage.

FIG. 18 shows a magnified view of the HAADF-STEM image of FIG. 15. Inthe figure, orderly lattice patterns were observed in the particle,confirming formation of the red phosphor of a monocrystalline structureby the foregoing producing method. Further, the red phosphor producedhad a good match with the orthorhombic system spatial point group Pmn2lmodel created by Rietveld analysis.

Example 3

Red phosphors of varying aluminum (Al) contents (the atom number ratiosy) within the composition formula (1) range were produced according tothe procedure described in Example 1. The atom number ratios of theelements other than aluminum (Al) were such that (y+9)/m=2.425, andx/m=3.75%. For comparison, a red phosphor containing no aluminum (Al)(the atom number ratio y=0) was also produced.

FIG. 19 represents the results of XDR analysis for each red phosphor. Itcan be seen from FIG. 19 that the peak position that occurs at eachdiffraction angle (2θ) shifts in one direction per peak position as thealuminum (Al) content (the atom number ratio y) is increased from y=0.For example, the peak near the diffraction angle 2θ=30.5 shifts towardsincreasing diffraction angles (20) with increase in aluminum (Al)content (the atom number ratio y). In contrast, the peak near thediffraction angle 2θ=35.5 shifts towards decreasing diffraction angles(2θ) with increase in aluminum (Al) content (the atom number ratio y).Specifically, it can be seen that the a and c axes in the orthorhombicsystem spatial point group Pmn21 extend while the b axis becomes shorteras the aluminum (Al) content (the atom number ratio y) increases. Thistendency was also confirmed at different atom number ratios m, x, and nwithin the composition formula (1) range.

This demonstrates that changes in the lattice space of the singlecrystal have occurred as a result of the aluminum (Al) in the redphosphor replacing silicon (Si) so as to constitute part of the singlecrystal. Specifically, it was confirmed that the red phosphor of singlecrystal contained aluminum (Al) that constituted part of the singlecrystal. Further, the red phosphor produced had a good match with theorthorhombic system spatial point group Pmn21 model created by Rietveldanalysis.

Example 4

Red phosphors of composition formula (1) were produced with varyingamounts of melamine according to the procedure described in Example 1.

FIG. 20 represents the luminous intensity of each red phosphor inrelation to the amount of melamine as a luminous intensity ratiorelative to the YAG:Ce phosphor.

As is clear from FIG. 20, the luminous intensity of the red phosphorvaries according to the amount of melamine added in the production ofthe red phosphor. Because the optimum value of melamine amount thatmaximizes the luminous intensity varies according to the proportions ofthe raw materials other than melamine, it is important to select anoptimum value for each raw material proportion, specifically, for eachcomposition ratio (1) of the red phosphor to be synthesized.

Example 5

A red phosphor of the composition formula (1) range was producedaccording to the procedure of Example 1, except that the heatingtemperature of the first heat-treatment step according to the proceduredescribed in Example 1 was varied. FIG. 21 represents the luminousintensity of the red phosphor, relative to the luminous intensity of theYAG:Ce phosphor.

It can be seen from FIG. 21 that the luminous intensity of the redphosphor varies with the heating temperature of the first heat-treatmentstep. Thus, in the production of the red phosphor of composition formula(1), it is preferable to optimize the heating temperature of the firstheat-treatment step. The preferable temperature was found to be about1,300° C.

Example 6

Red phosphors were produced as in Example 1, except that the rawmaterial compounds were mixed at the molar ratios presented in Table 3below according to the procedure described in Example 1. Red phosphorsof the composition formula (1) range were obtained in all samples exceptSi9-10. In Si9-10, an aluminum (A1)-free red phosphor of compositionformula (1) with y=0 was obtained.

TABLE 3 Amount of SrCO₃ EuN Si₃N₄ AlN melamine Sample No. (mol %) (mol%) (mol %) (mol %) added (mol %) Si9-01 42.7 11.8 35.5 10.0 60 Si9-0243.2 10.8 36.0 10.0 60 Si9-03 43.8 9.9 36.5 10.0 60 Si9-04 44.1 9.7 36.710.0 60 Si9-05 44.4 9.2 37.0 10.0 60 Si9-06 45.0 7.5 37.5 10.0 60 Si9-1340.0 10.0 40.0 10.0 60 Si9-14 41.4 9.7 38.9 10.0 60 Si9-15 42.8 9.4 37.810.0 60 Si9-16 44.1 9.2 36.7 10.0 60 Si9-17 45.3 8.9 35.8 10.0 60 Si9-1846.4 8.7 34.9 10.0 60 Si9-43 45.0 8.8 37.5  8.7 45 Si9-44 45.0 8.8 37.5 8.7 50 Si9-45 45.0 8.8 37.5  8.7 55 Si9-46 45.0 8.8 37.5  8.7 60 Si9-4745.0 8.8 37.5  8.7 65 Si9-48 45.0 8.8 37.5  8.7 70 Si9-10 47.9 10.0 42.1(0)  60 Si9-11 44.9 9.4 39.5  6.2 60 Si9-12 43.1 9.0 35.9 12.0 60

Emission spectrum was measured for each of the red phosphors produced asabove. Measurements were made using a spectrophotometer at an excitationwavelength of 450 nm and over the wavelength range of from 460 nm to 780nm. The results are presented in Table 4 below.

TABLE 4 Peak Peak wave- luminous Chroma- Chroma- Relative lengthintensity ticity ticity luminance Sample No. (nm) ratio (X) (Y) ratioSi9-01 673 1.23 0.685 0.314 0.89 Si9-02 672 1.28 0.683 0.317 1.00 Si9-03666 1.34 0.680 0.319 1.16 Si9-04 664 1.38 0.680 0.319 1.20 Si9-05 6671.42 0.679 0.320 1.27 Si9-06 660 1.27 0.676 0.324 1.26 Si9-13 665 0.850.679 0.320 0.73 Si9-14 667 1.22 0.683 0.316 0.97 Si9-15 667 1.35 0.6820.317 1.11 Si9-16 672 1.33 0.680 0.318 1.00 Si9-17 665 1.31 0.678 0.3211.13 Si9-18 666 1.22 0.677 0.322 1.12 Si9-43 673 0.98 0.671 0.327 0.93Si9-44 673 1.04 0.677 0.321 0.90 Si9-45 673 1.09 0.678 0.320 0.94 Si9-46662 1.25 0.674 0.324 1.27 Si9-47 662 1.34 0.678 0.321 1.31 Si9-48 6580.35 0.671 0.327 0.39 Si9-10 664 1.15 0.679 0.320 0.96 Si9-11 673 1.260.681 0.318 1.01 Si9-12 666 1.16 0.680 0.319 0.99 Luminous intensityratio is the relative value with respect to peak luminous intensity of(YAG:Ce) as the standard. Peak luminous intensity of (YAG:Ce)corresponds to 61 × 10{circumflex over ( )}5 cps. Relative luminanceratio is the relative value with respect to luminance of (CaS:Eu) as thestandard. Corresponds to 15% of (YAG:Ce) luminance ratio

For comparison, Table 5 below presents the measurement results for theYAG:Ce phosphor and CaS:Eu red sulfide phosphor used as standardphosphors.

TABLE 5 Peak Peak luminous Relative Sample as wavelength intensityChromaticity Chromaticity luminance standard (nm) ratio (X) (Y) ratioYAG: Ce 566 61 0.465 0.517 5.50 (Green standard) CaS: Eu 656 80 0.7020.296 1.00 (Red Sulfide standard)

As presented in Tables 3 and 4, the peak luminous intensity ratio of thered phosphor was 1.0 or more in samples Si9-01 to Si9-06, Si9-10 toSi9-12, Si9-14 to Si9-18, and Si9-44 to Si9-47.

The relative luminance ratio with respect to luminance of the CaS:Eu redsulfide phosphor as the standard (hereinafter, “relative luminanceratio”) was 1.0 or more in samples Si9-02 to Si9-06, Si9-Si9-11, Si9-15to Si9-18, Si9-Si9-46, and Si9-Si9-47.

Thus, in order to produce red phosphors with the peak luminous intensityratio of 1.0 or more, and the relative luminance ratio of 1.0 or more,each raw material needs to have the following component ratio, forexample.

-   -   Strontium carbonate: 42.8 mol % or more, and 46.4 mol % or less.    -   Europium nitride: 7.5 mol % or more, and 10.8 mol % or less.    -   Silicon nitride: 36.0 mol % or more, and 37.8 mol % or less.    -   Aluminum nitride: 8.7 mol % or more, and 10.0 mol % or less.

In addition, the amount of melamine added is 60 mol % or more, and 65mol % or less with respect to the total number of moles of the strontiumcarbonate, silicon nitride, europium nitride, aluminum nitride, andmelamine.

The component ratio of melamine is particularly important in theproducing method. As described above, melamine, with the melting pointof 250° C. or less, undergoes pyrolysis in the first heat-treatmentstep. The carbon (C) and hydrogen (H) generated by the pyrolysis ofmelamine bind to the oxygen (O) contained in the strontium carbonate,and produce carbon oxide gas (CO or CO₂) or H₂O. The carbon oxide gasand H₂O evaporate, and are removed from the first calcined product.Thus, the melamine should not be deficient or in excess.

For example, FIGS. 22 and 23 represent the results for Si-43 to Si-48presented in Tables 3 and 4. FIG. 23 represents peak luminous intensityas a function of the amount of melamine added. FIG. 23 representsluminance as a function of the amount of melamine added.

As is clear from FIG. 23, the peak luminous intensity ratio is 1.0 ormore for the melamine amount of from 45 mol % to 67 mol %.

Further, as is clear from FIG. 23, the relative luminance ratio is 1.0or more for the melamine amount of from 56 mol % to 68 mol %.

Thus, in the raw material proportions for Si-43 to Si-48, the melamineamount is preferably from 56 mol % to 68 mol %. It can be inferred fromFIGS. 22 and 23 that the melamine amount may have an addition of about±3 mol % above and below this range.

FIG. 24 represents the relationship between the amount of melamine addedand the remaining oxygen amount in the red phosphor. FIG. 25 representsthe relationship between the amount of melamine added and the remainingcarbon amount in the red phosphor.

As can be seen in FIG. 24, the oxygen content in the red phosphor varieswith changes in melamine amount.

The oxygen reduction in the red phosphor becomes particularly prominentwith the melamine amounts of 55 mol % and higher. This is because theoxygen in the strontium carbonate binds to the carbon or hydrogenproduced by the pyrolysis of melamine, and is removed in the form of,for example, carbon oxide gas (CO, CO₂, etc.) or H₂O.

However, when the melamine component ratio is as high as 70 mol %, theamount of carbon becomes excessively large with the excess amount ofremaining carbon after the melamine pyrolysis in the firstheat-treatment step. For example, the peak luminous intensity ratio is0.35, and the relative luminance ratio is 0.39 when the remaining carbonamount in the red phosphor is 0.1 wt %. Such residual carbon isconsidered to be partly responsible for the large reductions in luminousintensity and luminance.

It is therefore preferable that the melamine may be added in an amountof from 60 mol % to 65 mol %, as described above.

The particle size of the red phosphor depends upon the amount ofmelamine added. As represented in FIG. 26, the particle size of the redphosphor decreases with increase in melamine amount. For example, theaverage particle size of the red phosphor was about 5 μm with themelamine amount of 45 mol %, about 3.7 μm with the melamine amount of 60mol %, and about 3.5 μm with the melamine amount of 65 mol %.

As demonstrated above, the melamine amount is important in terms of easeof production of a fine powdery red phosphor.

Addition amount of europium nitride was examined. Based on Tables 3 and4, FIG. 27 represents the relationship between the peak luminousintensity of the red phosphor and the amount of europium nitride, andFIG. 28 represents the relationship between the luminance of the redphosphor and the amount of europium nitride.

As is clear from FIG. 27, the peak luminous intensity ratio is 1.0 ormore when the europium nitride amount is from about 7.0 mol % to about12.0 mol %.

As is clear from FIG. 28, the relative luminance ratio is 1.0 or morewhen the europium nitride amount is from 7.0 mol % to 11.0 mol %.

However, as can be seen from Tables 3 and 4, there are cases where, asin sample Si9-13, the peak luminous intensity ratio is 0.85 even withthe europium nitride amount of 10.0 mol %. This is believed to be due tothe small amount of strontium carbonate added. As in this case, theeuropium nitride amount may be influenced by the amounts of other rawmaterials. Considering this, the europium nitride amount is morepreferably from 7.0 mol % to 12.5 mol %.

Based on Tables 3 and 4, FIG. 29 represents peak luminous intensitydistribution with varying ratios of strontium carbonate, europiumnitride, and silicon nitride under the fixed melamine and aluminumnitride ratios of 60 mol % and 10.0 mol %, respectively. The figure isshown with sample numbers and peak luminous intensity values.

As shown in FIG. 29, samples Si9-01 to Si9-06, and samples Si9-15 toSi9-18 had peak luminous intensity ratios of 1.2 and higher. Inparticular, samples Si9-03 to Si9-05 and samples Si9-15 to Si9-17 hadhighly desirable peak luminous intensity ratios of 1.3 and higher.

The red phosphor of sample Si9-47 with the emission peak wavelength of662 nm was examined with regard to its X-ray diffraction pattern forCu—Kα radiation, using a powder X-ray diffractometer available fromRigaku Corporation. The result is shown in FIG. 30. Specifically, thefigure represents the crystal structure of the phosphor. From the X-rayanalysis pattern, it was confirmed that the red phosphor obtained by theforegoing producing method was of the orthorhombic system spatial pointgroup Pmn21.

Example 7

Red phosphors were produced using the additional raw material compoundcalcium nitride (Ca₃N₂) according to the procedure of Example 1. The redphosphors were produced as in Example 1, except that the raw materialcompounds were mixed at the molar ratios presented in Table 6 below.

TABLE 6 Amount of melamine Ca₃N₂ SrCO₃ EuN Si₃N₄ AlN added (Si9) (mol %)(mol %) (mol %) (mol %) (mol %) (mol %) Si9—Ca01 0 44.2 9.2 44.2 9.8 60Si9—Ca02 4.5 34.7 10.0 40.1 10.7 60 Si9—Ca03 7.0 29.4 10.5 42.0 11.2 60Si9—Ca04 9.8 23.5 11.0 44.0 11.7 60

Emission spectrum was measured for each of the red phosphors produced asabove. Measurements were made using a spectrophotometer at an excitationwavelength of 450 nm and over the wavelength range of from 460 nm to 780nm. The results are presented in Table 7 below.

TABLE 7 Peak Peak wave- luminous Chroma- Chroma- Relative lengthintensity ticity ticity luminance (Si9) (nm) ratio (X) (Y) ratioSi9-Ca01 664 1.31 0.680 0.320 1.12 Si9-Ca02 678 1.30 0.685 0.315 0.88Si9-Ca03 679 1.24 0.688 0.312 0.73 Si9-Ca04 684 1.18 0.690 0.310 0.63

As can be seen in Tables 6 and 7, it was confirmed that the peakemission wavelength shifts towards the longer wavelength side withincrease in calcium nitride amount. For example, the peak emissionwavelength was 664 nm when no calcium nitride was added. The peakemission wavelength was 678 nm with the calcium nitride amount of 4.5mol %, 679 nm with the calcium nitride amount of 7.0 mol %, and 684 nmwith the calcium nitride amount of 9.8 mol %.

However, the luminance decrease tended to become more prominent as thecalcium nitride amount was increased. Thus, while the addition ofcalcium nitride can shift the peak emission wavelength, sufficient caremust be taken not to lower the luminance.

When the calcium nitride amount is 9.8 mol % or less, or when thecalcium nitride was not added, luminous intensity with the peak luminousintensity ratio of 1.0 or more was obtained. Further, luminous intensitywith the peak luminous intensity ratio of 1.18 was obtained even whenthe amount of calcium nitride compound was 9.8 mol %.

Thus, it can be said that the calcium nitride amount does not haveserious effects on luminous intensity, as long as it falls within theforegoing range.

In the red phosphor producing method, the ratios of strontium carbonate(SrCO₃), europium nitride (EuN), silicon nitride (Si₃N₄), aluminumnitride (AlN), and melamine (C₃H₆N₆) can be set within the followingmaximum ranges by adjusting the ratio of each raw material compound.

-   -   Strontium carbonate: 23.5 mol % or more, and 47.0 mol % or less.    -   Silicon nitride: 33.0 mol % or more, and 41.0 mol % or less.    -   Europium nitride: 7.0 mol % or more, and 12.5 mol % or less.    -   Aluminum nitride: at least contained in an amount of 12.0 mol %        or less.

In addition, the melamine is added in an amount of from 60 mol % to 65mol % with respect to the total number of moles of the strontiumcarbonate, silicon nitride, europium nitride, and aluminum nitride.

In the red phosphor producing method, melamine is used as the carbonsource. However, for example, organic substances containing carbon,hydrogen, and nitrogen may be used instead of the melamine.Oxygen-containing organic substances are not preferable. A carbon powderalso can be used instead of the melamine.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

The invention claimed is:
 1. A red phosphor comprising: an element A,europium (Eu), silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N)at the atom number ratio of the composition formula (1)[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1), wherein the element A in the composition formula (1) is at leastone of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba),and m, x, y, and n in the composition formula (1) satisfy the relations0.5<m<5, 0<x<1, 0<y<1, and 0<n<10 wherein the compound of thecomposition formula (1) has a crystal structure that belongs to anorthorhombic system spatial point group Pmn2₁.
 2. The red phosphor ofclaim 1, wherein the element A is strontium (Sr).
 3. A method forproducing a red phosphor comprising: preparing a carbonate compound ofan element A, europium nitride, silicon nitride, and aluminum nitride soas to contain the element A, europium (Eu), silicon (Si), and aluminum(Al) at the atom number ratio of the composition formula (1) below, andmixing melamine to produce a mixture,[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1), wherein the element A in the composition formula (1) is at leastone of magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba),and m, x, y, and n in the composition formula (1) satisfy the relations0.5<m<5, 0<x<1, 0<y<1, and 0<n<10 wherein the compound of thecomposition formula (1) has a crystal structure that belongs to anorthorhombic system spatial point group Pmn2₁; and calcining themixture; and pulverizing a calcined product of the mixture.
 4. Themethod for producing the red phosphor of claim 3, wherein the calciningof the mixture, and the pulverization of the calcined product of themixture are repeated.
 5. A white light source comprising: ablue-emitting diode formed on an element substrate; and a kneadedproduct disposed on the blue-emitting diode, and provided as a productof a red phosphor and a green phosphor kneaded in a transparent resin,wherein the red phosphor contains an element A, europium (Eu), silicon(Si), aluminum (Al), oxygen (O), and nitrogen (N) at the atom numberratio of the composition formula (1)[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−(n−m)/3])  Composition Formula(1), where the element A in the composition formula (1) is at least oneof magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and m,x, y, and n in the composition formula (1) satisfy the relations0.5<m<5, 0<x<1, 0<y<1, and 0<n<10 wherein the compound of thecomposition formula (1) has a crystal structure that belongs to anorthorhombic system spatial point group Pmn2₁.
 6. An illuminating devicecomprising: a plurality of white light sources disposed on anillumination substrate, wherein the white light sources each include: ablue-emitting diode formed on an element substrate; and a kneadedproduct disposed on the blue-emitting diode, and provided as a productof a red phosphor and a green phosphor kneaded in a transparent resin,and wherein the red phosphor contains an element A, europium (Eu),silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N) at the atomnumber ratio of the composition formula (1)[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1), where the element A in the composition formula (1) is at least oneof magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and m,x, y, and n in the composition formula (1) satisfy the relations0.5<m<5, 0<x<1, 0<y<1, and 0<n<10 wherein the compound of thecomposition formula (1) has a crystal structure that belongs to anorthorhombic system spatial point group Pmn2₁.
 7. A liquid crystaldisplay device comprising: a liquid crystal display panel; and abacklight using a plurality of white light sources that illuminate theliquid crystal display panel, wherein the white light sources eachinclude: a blue-emitting diode formed on an element substrate; and akneaded product disposed on the blue-emitting diode, and provided as aproduct of a red phosphor and a green phosphor kneaded in a transparentresin, and wherein the red phosphor contains an element A, europium(Eu), silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N) at theatom number ratio of the composition formula (1)[A_((m−x))Eu_(x)]Si₉Al_(y)O_(n)N_([12+y−2(n−m)/3])  Composition Formula(1), where the element A in the composition formula (1) is at least oneof magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and m,x, y, and n in the composition formula (1) satisfy the relations0.5<m<5, 0<x<1, 0<y<1, and 0<n<10 wherein the compound of thecomposition formula (1) has a crystal structure that belongs to anorthorhombic system spatial point group Pmn2₁.